1. Field of the Invention
This invention relates to a compressed air pressure supply system used in compressed air systems, such as an air brake system for a vehicle.
2. Prior Art
A conventional compressed air pressure supply system generally comprises, as disclosed in U.S. Pat. No. 4,544,385, a dryer device for drying the compressed air delivered from an air compressor, the dryer device having a recoverable desiccant therein. This system also includes a governor device regulating the pressure inside the air reservoir in which the dried compressed air having passed through said dryer device is stored. The system further comprises a purge reservoir for storing some of the dried compressed air from said dryer device and, a regenerating valve controlled by said governor. The purpose of the regenerating valve is to shut and open, with respect to the atmosphere, the interior of said dryer device so that, when this valve is open, the dried compressed air in said purge tank returns to the dryer device while the water particles having adhered to the desiccant are discharged into the atmosphere to regenerate said desiccant. At the same time, the residue including residual oil particles on the bottom of the vessel is drained to the exterior.
Thus, the conventional system is designed so that the compressed air delivered from the air compressor device is directly introduced to the dryer device. Moreover, the regenerable desiccant will not be fully recoverable even when recovered in the aforementioned matter, when acting highly hygroscopically it attracts oil particles, so that the drying power thereof becomes reduced. Contamination of the desiccant by oil particles occurs to a very serious extent, in particular, when the unloader of the air compressor device is switched over to the loading condition and the oil particles having accumulated in the air compressor device are suddenly supplied. Such contamination due to said residue also arises when residues have formed in large quantities.
A conceivable means of preventing such contamination of the desiccant by oils and residues is to mount an oil separator upstream of the dryer device. However, even with the installation of an oil separator such desiccant contamination will not be avoidable due to a deterioration in the performance of said oil separator as a result of prolonged use. It is self-evident that the problem would be resolved if the desiccant were replaced at regular short intervals, but this would be inconvenient and would give rise to a need to continue the drying operation at a reduced drying efficiency without regular desiccant replacement if the desiccant were used in areas in which the desiccant is not easy to obtain.